Donald Trump smiles at left as Republican presidential candidate, former House Speaker Newt Gingrich talks to media after their meeting in New York, in this December 2011 file photo. Whom will Trump endorse for president, Newt Gingrich or Mitt Romney?

Now CNN is reporting that The Donald will go for Mitt. Will it be the insurgent or the front-runner? Stay tuned for Mr. Trump’s 12:30 p.m PST (3:30 p.m. Eastern time) press conference in Las Vegas. It’s like an episode of “Celebrity Lessons in How to Get Attention.”

In the short run, it might give either Mr. Romney or Mr. Gingrich a boost in Nevada. For one thing, it would get lots of press attention, because reporters flock to anything Trump like moths toward a flaming toupee. Trump remains popular in tea party circles, so it might bolster the endorsee’s conservative credentials. Most important, it might draw some support in Las Vegas, gambling mecca. Trump is a gambling mogul, after all.

But the long run? At best, it’s a wash. Romney has got so many endorsements that it would be just one more name on his shelf. Gingrich could use it more, though it now looks as if he’s going to finish second in this contest, as well. More likely, it’s a nod that could damage its recipient. There’s a reason that only two GOP contenders, Gingrich and Rick Santorum, agreed to attend a Newsmax debate that Trump was supposed to host last December, before it was canceled. The other contenders weren’t going to touch that event with a 10-foot comb.

Yes, Trump briefly led GOP polls back when he was publicly toying with a run. (Or, publicly toying with a run more than he is now, since he’s continued to hint he might jump in.) But he sank faster than a bad gambler’s fortune. By last April, a Gallup poll showed that 64 percent of Americans said they would definitely not vote for Donald Trump. That’s a very high unfavorable rating.

Plus, a Trump endorsement is actually a net negative, according to a January Washington Post/Pew poll. Twenty percent of Republican and Republican-leaning respondents to this survey said a Trump endorsement would make them less likely to vote for the candidate in question. Seventeen percent said it would make them more likely to vote for the endorsee.

Trump will say almost anything, and has, and that would be a problem for Romney, or whomever Trump backs. The endorsee will be asked about the birther thing, for instance – Trump got lots of mileage out of questioning whether President Obama was born in the US. He’ll be asked whether he shares Trump’s view that the US needs to slap tariffs on imports from China (thereby raising the price of every item in Walmart at a stroke.)

Trump is unpredictable – just look at the confusion over who his favored choice actually is. If we were putting down our money – and we’re not – we’d say this is one wager that isn’t going to produce a row of cherries across the slot machine, electorally speaking.